Question

Copper in saltwater near the discharge of a sewage treatment plant is determined by first seperating and concentating it by solvent extraction of its dithizone chelate at pH 3 into methylene chloride and then evaportation the solvent, ashing the chelate to dstory the organic portion, and titrating the coperwith EDTA. Three 1 liter portions of the sample are each extracted with 25mL portions of methylene chloride and the extraction combined and diluted to 100mL. A 50 mL aliquot is evaporated, and ashed. A 5mL aliquot of water is added and the solution titrated. The EDTA solution has CaCO3 titer of 2.69 mg/mL and 2.67 is required for titration of the copper.

You have beakers, graduated cylinders, measuring pipets, volumetric pipets, burets and columetric flasks to make the measurements. For each of the measurements in bold print, identify the proper piece of glassware to make the measurement. Justify your chooses.

Answer 1

1 liter, 100 mL and 50 mL can be measured by using columetric flasks of corresponding volumes. This will provide reasonable accuracy in measuring volume. Beakers or graduated cylinders cannot be used as they are less accurate.

25 mL can be measured using graduated cylinder which will provide reasonable accuracy.

5 mL can be measured using volumetric pipette for high accuracy.

2.67 can be measured using burette which is convinent and reasonably accurte for titration.